Conventionally, various methods of determining whether knocking (knock) is present or absent have been proposed. For example, there is a technique of determining occurrence of knocking based on whether or not magnitude of vibration detected in an internal combustion engine is greater than a knocking determination value. A knock control device for an internal combustion engine disclosed in Japanese Patent Laying-Open No. 2003-21032 includes: a knock sensor detecting knocking in an internal combustion engine; a statistical processing portion statistically processing an output signal detected by the knock sensor; a first temporal determination portion determining occurrence of knocking based on a processing result by the statistical processing portion; a second temporal determination portion determining occurrence of knocking based on a waveform shape of the output signal detected by the knock sensor, and a final determination portion finally determining occurrence of knocking based on the knock temporal determination of the first temporal determination portion and the knock temporal determination of the second temporal determination portion. When both of the first and second temporal determination portions determine that knocking has occurred, the final determination portion finally determines that knocking has occurred. In the first temporal determination portion, a maximum value of output signals detected by the knock sensor and a knock determination level (knock determination value) calculated based on the processing result by the statistical processing portion are compared with each other, whereby whether knocking has occurred or not is determined. Based on the occurrence frequency of knocking, the knock determination value is corrected to be a value obtained by subtracting a setting value ΔV from the knock determination value, or to a value obtained by adding a product of a value A, which is greater than “1”, and setting value ΔV to the knock determination value.
According to the knock control device disclosed by the publication, a knock temporal determination by the statistical processing program and a knock temporal determination by the waveform shape program are used, and only when both of the temporal determinations determine that knocking has occurred, it is finally determined that knocking has occurred. As a result, occurrence of knocking can precisely be determined even as to an output signal with which knocking has been erroneously detected by a knock determination employing solely the statistical processing program or the waveform shape program.
However, in the knock control device of Japanese Patent Laying-Open No. 2003-21032, when the knock determination value is corrected based on the occurrence frequency of knocking, setting value ΔV being the correction amount of the knock determination value or the product of “A” and setting value ΔV is constant. Therefore, when the correction amount of the knock determination value is small, it is necessary to correct the determination value for several times and it takes time until a knock determination value with which occurrence of knocking is precisely determined and the ignition timing is precisely controlled. Thus, there has been a problem that ignition timing may not be retarded appropriately when knocking has occurred, or ignition timing may not be advanced appropriately when knocking has not occurred.